Category Archives: laser scan

Sometimes, at a distance, when the sunlight hits Corfe Castle… it seems whole again..

Just an illusion..it has been a battered shell since 1646, when, after a long siege, it was captured and blown apart by the Parliamentarians.

They made sure that the supporters of King Charles could not use it again..unpicking the defenses, trenching under the walls, packing with gunpowder and throwing the turrets and walls in all directions.

But this blog is also about something that happened 300 years earlier ..when Corfe Castle was one of the brightest and best within the league table of medieval fortresses.

About 1250, the 1st Tower was created for King Henry III.

When first added to the defensive circuit, this structure was a cutting edge design, built to protect the southern and western approaches. The barons were often restless.

A wonderful thing, with its rounded tower and its 3 arrow loop embrasures.. from these, bowmen or more probably cross bowmen could take aim and fell an attacker up to 300m away. A crossbow bolt could penetrate a knight’s armour.

We only know of one illustration and then only in plan.. drawn for the new owner Sir Christoper Hatton..14 years after it was sold to him by Elizabeth I. Such castles were old fashioned by then.

Ralph Treswell’s 1586 survey of Corfe Castle shows the 1st Tower between the steps up to the Outer Gatehouse (right) and the Outer Bailey latrines (left). 60 years later it was blown in two.

The Parliamentary demolition team searched for weak spots and made them weaker. They set their charges and the explosion fractured the 1st tower.. right down its central arrowloop. It must have sounded like an earthquake in the town.. and when the dust settled, the east half leaned drunkenly outward and the west half had been flipped 180 degrees coming to a rest half way down the hill slope.. This is where it has remained gathering soil, vegetation and scrub for another 371 years.

Looking along the west wall of the Outer Bailey from the SW Gatehouse towards Corfe Village. The scrub covered fallen 1st Tower lies below the castle wall hidden by vegetation directly below the position of the church tower.

Other parts of the Castle have been cleaned and consolidated over the years but the chunks that lie tumbled across the slopes, or down by the river, have not. The largest of these pieces is the First Tower, and now …the scaffolding is upon it.

So last week I headed south through a cold winter morning of dramatic contrasts: on the high chalk downs, bright melting sunlight above vales of mist.. but down on the heath, thick freezing fog and brittle white frosted trees.

The caged Tower loomed but nobody was on it. I found them in the tea rooms beside the Outer Bridge. Architects, builders and property staff… after warm drinks we headed for the vertical ladder up from the ditch.

The route up to the First Tower from the Castle Ditch. The standing half of the tower is on the right with part of the 13th century cross-loop visible, the other half is part buried beneath the lowest scaffolding.

A good time to visit. Most of the centuries of roots and soil had been removed. We climbed over the scaffolding and saw, up close, the medieval construction, types of mortar, the galleting of the joints and the different beds of Purbeck stone, the arrangement of rubble and fine ashlar.

But everything in reverse. When we got to the top, we saw the great slabs of Purbeck Marble laid down as foundation layers before the tower proper was built above. Someone saw tool marks around their edges and suggested they may have been recycled coffin cover rough-outs.

The foundation of the Tower made of large long slabs of stone, then rough block work, not meant to be seen, followed by the finely worked ashlar burr stone forming the battered plinth (three course vertical, three at 60 degrees and then vertical again rising to the top of the rounded tower).

A stranded whale of a thing, its construction now more visible than at any time since it was built.

Could we laser scan it and capture this revelation in time?

Yes it can be done.

It will be partly obscured soon, new mortar and capping needs to be placed over the Tower to protect the newly exposed structure from weathering.

Both halves will be digitised.

The scaffolding will be edited out, and then, by the touch of a button… the First Tower will be reunited again.

You will need to go to Badbury Rings in Dorset and head to the west side of the outer rampart. Stand where the great Roman road, known as the Ackling Dyke, touches the hillfort and then look north.

From the Badbury Roman cross-roads take the road to Old Sarum (nr Salsibury) where there is another hillfort at another cross-roads. After the Roman conquest, just like at Badbury, a small Roman town grew up nearby. At Badbury it’s Shapwick (Vindocladia) at Old Sarum its Stratford sub Castle (Sorviodunum).

The Roman administration lasted about 400 years then the troops left for the continent and Britain sorted out its own politics. It broke up into factions, petty political infighting and one by one these new Romanised British states caved in to alien cultures from outside the old empire. Our modern counties tell the story of conflict and the place names of our villages and towns in the east are almost exclusively Anglo-Saxon. Bit by bit the Roman centres were abandoned or taken over. In recent years it has been suggested that British and Germanic incomers integrated more amicably than has traditionally been believed…but ancient DNA compared with DNA from modern populations argues for the old fashioned view …that the Brits were ethnically cleansed from the east.

The Saxons took Old Sarum in AD 552, their history book, the Anglo-Saxon Chronicle, states this. A worrying time for the Romanised peoples of Dorset and Somerset. Time to block the Ackling Dyke. It was too easy an access route for the invaders. The old earthwork marking the Dorset border, Bockerley Dyke, was strengthened and the road was blocked here (General Pitt Rivers discovered this during his excavations in 1890). It was re-opened again soon afterwards…

Early aerial photograph of Badbury Rings (Wessex from the Air 1928). The Ackling Dyke runs top centre to centre left. Notice the way the outer rampart touches the road and covers its south eastern bank and ditch. The Devil’s Footprint is top centre cutting the road at right angles. The line has subsequently been rebuilt but over the years has slumped into the old cutting.

Badbury at the cross-roads needed re-fortification. Imagine standing here in the 6th century.. can you feel the vulnerability. What happened?

There are three ramparts around the hillfort. The two inner ones lie close together and look similar…they are Iron Age. What about the outer one? It is further out, slighter, bit humpy…unfinished?. Some say it was built about AD 44 ..on the eve of the Roman Conquest, but stand on the west edge where it runs beside the Ackling Dyke and look at the earthworks.

Which came first? The great Ackling Dyke is 25m across. Late Roman banks and ditches flank the road on either side. Recent LiDAR laser scans, along with aerial photographs, show something new. The east road bank is cut by Badbury’s outer ditch. Excavation at Shapwick has shown that the road is late 4th century…so Badbury’s rampart is later still. Last week I visited and saw it on the ground.

Then there is the chalk quarry just a little to the north.. known as the Devil’s Footprint. It runs from the rampart across the line of the road to the steeper slope to the west. Once it was covered in gorse but NT rangers have now made the earthwork clearly visible and it is not a random digging. It cuts the Ackling Dyke at a right angle. A wide formidable defence acting as a cross-ridge dyke.

Back in 2004, we radiocarbon dated the re-occupation of the hillfort to the 5th century, so good evidence that Badbury’s people re-made this place as a fortress. The British Dorset militia quickly threw up Badbury’s outer rampart and dug the wide trench, the ‘Devil’s Footprint’,to hold back the Saxon tide…. well..now..as the archaeology of the earthworks has demonstrated, there’s a strong argument to be made for this.

Killerton near Exeter Devon is a large farming estate. The Acland family gave it to the National Trust in the 1940s along with their Exmoor Holnicote Estate.

Killerton was where the main house was and generations of the family lived there. If you go there today you’ll see the house nestled beneath Dolbury hillfort and surrounded by mature wooded parkland.

Killerton House with Dolbury Hill behind

In the medieval period, the old centre of the Estate lay to the west, beside the river at Columbjohn. There is still a chapel there where some of the Aclands are buried… but 250 years ago Sir Thomas Acland wanted a new grand house and shifted his home to a new location.

The chapel near the old manor house site at Columbjohn

I had a meeting a couple of weeks ago. It was to discuss the recent archaeological recording work and repair along Killerton’s scheduled park boundary wall.

When I got there I was shown a LiDAR image of the park. The amazing thing about LiDAR is that it can strip away the trees and show the archaeological earthworks hidden beneath. As the plane flies over, it fires numerous laser impulses at the ground. The first return hits the tree canopy but the second return is from the laser impulses that filter though and bounce off the ground beneath. The thing to do is to filter out the first returns and there is your picture of the archaeology on the forest floor.

The LiDAR showed something very strange in Columbjohn Wood. A big rectangular feature on the ridge top with an L-shaped feature to the west.

There was time. Friday afternoon, a bright clear winter day, leafless and no undergrowth. I set off on a ground-truthing exercise. Up past the mansion house, through the garden and the parkland edge, crossing the boundary into Columbjohn Wood. Then through the trees and along the ridge top looking at the ground beneath my feet (archaeologists tend to look at the ground).

The ditch and stone revetted boundary bank of the 18th-century deer park

Great views out to the south.. and there was the conical Mount Pleasant, which, I had been told, had the foundations of a hexagonal garden folly tower on it. Worth having a look….

…a great location and the stone footings were still clear jutting from the top of a barrow-like mound. The folly tower would once have been clearly visible in the surrounding landscape but not really from the present Killerton House.

Mount Pleasant from Columbjohn Wood with the folly mound on the top

Back down the hill and then up to Columbjohn Wood ridge again and ..there were some clay roof tiles churned up in an animal burrow and ..there was the L-shaped rampart and a large rectangular pit. A track cut close to its north side and here I bumped into a spread of brick rubble eroding out of the wheel ruts… Amongst the trees were scattered chunks of stone.

Interesting…

The site? of Sir Thomas Acland’s never completed mansion in Columbjohn Wood.

I spoke to Denise at Killerton House. She told me that it might be the house that Sir Thomas Acland changed his mind about.

1775-76: in America, the British colonists had chosen to disconnect themselves from the mother country and at Killerton, Sir Thomas had chosen the location for his new house. He appointed a fashionable architect James Wyatt and work began.

The Acland family archive contains the accounts for £1000s spent on building work.. creating the cellars and beginning to construct the walls, but something went wrong. There’s a terse exchange of letters in early 1777. Mr Wyatt was to cease all work and the builders were to leave the new site.

Everything stopped. Then the work began again in 1778-9 but at a different site and with Mr Johnson not Mr Wyatt. The accounts tell of payments to the salvage team, 33 men taking down bricks from the site on the hill and unpicking the mortar. Loading the materials onto carts to bring to the new site where Killerton House is today.

Nobody had worked out where this almost mansion was but it seems that the LiDAR has found it for us. Our big rectangular pit may be the cellars mentioned in the documents and the pile of stuff to one site may be unwanted building material left behind during the salvage work.

Old oak at the foot of Mount Pleasant

Perhaps this 1775-6 site was a windier location… but with great views across the Devon landscape and with the hill top tower folly clearly visible in the foreground. I wonder why Sir Thomas changed his mind.

Why can’t we keep it open? We just can’t. It would quickly be mashed by Chedworth’s winter frosts. Weeds would colonise the tesserae and roots break up the pattern. We can’t expose something and allow it to be trashed. So the last day was backfill day.

Bill and his team setting up the laser scanner to make a 3D record of the mosaic surface. Interesting Dr Who style white station orbs.

Nancy had sourced the right sort of cover fabric. Nicki had got it sent by courier to make sure it arrived on time. While I completed the site record, drawing the plans and sections and writing up the context sheets, Nancy organised the covering. Sandbags were filled with topsoil to support the mosaic edges and fine topsoil was placed on the terram sheet.

Visitors hurried from reception to get a last glimpse before the mosaic was consigned to the dark once again. 150 years since its first discovery.

While drawing the plan of the site we found a mottled stone which on closer inspection turned out to be a piece of Italian marble. An exotic material brought to the villa to decorate an architectural feature or perhaps part of a panel on a piece of furniture.

So with all this highly accurate digital recording why measure and draw it the old fashioned way? Well.. it’s all about relationships. One has to touch the soil, by measuring you question what you seen. The closer you look, the more you understand and spotting something on a scan once the site is backfilled is too late. That’s my excuse for playing around with tape measures and a drawing board while 11 days of spoil were being heroically relocated in a single day.

A light misty rain fell every now and then, making drawing difficult. I measured a piece of stone which I thought at first was slate but turned out to be a corner piece from an Italian marble panel. Proving again that this place was an opulent mansion and we now see only the bare bones of something which was once quite magnificent.

The last pieces of excavation in room ‘e’ revealed that the wall was later than the east -west wall on the right but earlier than the colonnade wall (top left) because it runs under it. Water probably entered the feature from the baths (top left) and drained out of the centre of the east side (bottom right).

The water feature in ‘e’ became even more confusing when I asked Rob to make a narrow trench to link his 1.2m square trench in the south-west corner of the building towards the mosaic to the north. The square trench had been filled with Victorian backfill 1.0m deep from top to bottom but the northern extension found a Roman mortar floor at 0.4m and by making the north side of the square trench vertical it became clear that our trench had copied the Victorian exploratory trench and everything north of it appeared to be undisturbed Roman.

Too late to understand it better. The north extension did not find a flight of steps into a bath but a rough mortar shelf with fragments of blue lias slabs crushed into its surface. We can imagine a supply of used water from the baths entering this feature from the north and perhaps surrounding a statue or fountain within the building before leaving via the drain we know about on the east side. We know a bit more about this feature now but not enough. We need to look around for some comparisons.

Rob’s trench across our ‘water feature’ in ‘e’.He extended his 1.2m square trench in its SW corner north towards the mosaic room wall. The big block of stone is part of the late Roman colonnade wall which is contemporary with the mosaic. It runs over an earlier wall line which you can see at the end of the trench on the right hand side of the stone. Rob’s extension picked up an uneven mortar floor which sloped down towards the square trench and has blue lias stone slabs broken onto its surface. The filling of the square trench had all been Victorian backfill but by cleaning the north trench wall back the Roman mortar surface could be seen overlying a compacted clay layer. So there was a Roman platform of clay and mortar extending into the walled ‘water feature’ Had the Victorians dug through it or was the south side meant to be deeper. Over 1.0m deep from the wall top to the stone and mortar base.

Sir Ian Richmond’s walls did exist. Sometimes they were buried quite deep below his concrete but they existed. We did not prove or disprove the interpretations as early baths he gave them.

A trench to test one of Sir Ian’s walls. This one lay 0.3m deeper than the base of his interpretive concrete walls. The line of the buried wall would have continued east under the centre of the ‘Reception Room’ mosaic. Our extension trench only found the mortar bedding for the mosaic with one or two fragments at the edges.

Finally I was finished with the recording and threw myself fresh into the backfilling and hit a wall of congealed rubble, mud and clay. The rain had mingled with the spoil heap, seeped down to the waterproof tarpaulin fusing it into an unyielding barrier. Shifting it was very hard work but everyone worked so hard to put it back where it came from and eventually we saw the grass again and the vast heap of dirt had gone.

This is the earliest layer we reached a cobbled floor surface which is covered by the ‘water feature’ west wall which itself pre-dates the mosaic floor.

Thank you so much to everyone who helped over the two weeks and all the encouragement of the Chedworth staff and volunteers and of course the visitors who cheered us on…but Nancy and I would particularly like to thank the Bank Cottage stalwarts Harry, Carol, Kate and Fay.